Calculated beam quality correction factors for ionization chambers in MV photon beams.

The beam quality correction factor, [Formula: see text], which corrects for the difference in the ionization chamber response between the reference and clinical beam quality, is an integral part of radiation therapy dosimetry. The uncertainty of [Formula: see text] is one of the most significant sources of uncertainty in the dose determination. To improve the accuracy of available [Formula: see text] data, four partners calculated [Formula: see text] factors for 10 ionization chamber models in linear accelerator beams with accelerator voltages ranging from 6 MV to 25 MV, including flattening-filter-free (FFF) beams. The software used in the calculations were EGSnrc and PENELOPE, and the ICRU report 90 cross section data for water and graphite were included in the simulations. Volume averaging correction factors were calculated to correct for the dose averaging in the chamber cavities. A comparison calculation between partners showed a good agreement, as did comparison with literature. The [Formula: see text] values from TRS-398 were higher than our values for each chamber where data was available. The [Formula: see text] values for the FFF beams did not follow the same [Formula: see text], [Formula: see text] relation as beams with flattening filter (values for 10 MV FFF beams were below fits made to other data on average by 0.3%), although our FFF sources were only for Varian linacs.

Establishing the European diagnostic reference levels for interventional cardiology.

Interventional cardiac procedures may be associated with high patient doses and therefore require special attention to protect the patients from radiation injuries such as skin erythema, cardiovascular tissue reactions or radiation-induced cancer. In this study, patient exposure data is collected from 13 countries (37 clinics and nearly 50 interventional rooms) and for 10 different procedures. Dose data was collected from a total of 14,922 interventional cardiology procedures. Based on these data European diagnostic reference levels (DRL) for air kerma-area product are suggested for coronary angiography (CA, DRL = 35 Gy cm2), percutaneous coronary intervention (PCI, 85 Gy cm2), transcatheter aortic valve implantation (TAVI, 130 Gy cm2), electrophysiological procedures (12 Gy cm2) and pacemaker implantations. Pacemaker implantations were further divided into single-chamber (2.5 Gy cm2) and dual chamber (3.5 Gy cm2) procedures and implantations of cardiac resynchronization therapy pacemaker (18 Gy cm2). Results show that relatively new techniques such as TAVI and treatment of chronic total occlusion (CTO) often produce relatively high doses, and thus emphasises the need for use of an optimization tool such as DRL to assist in reducing patient exposure. The generic DRL presented here facilitate comparison of patient exposure in interventional cardiology.

Characterisation of grids of point detectors in maximum skin dose measurement in fluoroscopically-guided interventional procedures.

PURPOSE: Point detectors are frequently used to measure patient's maximum skin dose (MSD) in fluoroscopically-guided interventional procedures (IP). However, their performance and ability to detect the actual MSD are rarely evaluated. The present study investigates the sampling uncertainty associated with the use of grids of point detectors to measure MSD in IP. METHOD: Chemoembolisation of the liver (CE), percutaneous coronary intervention (PCI) and neuroembolisation (NE) procedures were studied. Spatial dose distributions were measured with XR-RV3 Gafchromic(®) films for 176 procedures. These distributions were used to simulate measurements performed using grids of detectors such as thermoluminescence detectors, with detector spacing from 1.4 up to 10 cm. RESULTS: The sampling uncertainty was the highest in PCI and NE procedures. With 40 detectors covering the film area (36 cm × 44 cm), the maximum dose would be on average 86% and 63% of the MSD measured with Gafchromic(®) films in CE and PCI procedures, respectively. In NE procedures, with 27 detectors covering the film area (14 cm × 35 cm), the maximum dose measured would be on average 82% of the MSD obtained with the Gafchromic(®) films. CONCLUSION: Thermoluminescence detectors show good energy and dose response in clinical beam qualities. However the poor spatial resolution of such point-like dosimeters may far outweigh their good dosimetric properties. The uncertainty from the sampling procedure should be estimated when point detectors are used in IP because it may lead to strong underestimation of the MSD.

Measurement of maximum skin dose in interventional radiology and cardiology and challenges in the set-up of European alert thresholds.

To help operators acknowledge patient dose during interventional procedures, EURADOS WG-12 focused on measuring patient skin dose using XR-RV3 gafchromic films, thermoluminescent detector (TLD) pellets or 2D TL foils and on investigating possible correlation to the on-line dose indicators such as fluoroscopy time, Kerma-area product (KAP) and cumulative air Kerma at reference point (CK). The study aims at defining non-centre-specific European alert thresholds for skin dose in three interventional procedures: chemoembolization of the liver (CE), neuroembolization (NE) and percutaneous coronary interventions (PCI). Skin dose values of >3 Gy (ICRP threshold for skin injuries) were indeed measured in these procedures confirming the need for dose indicators that correlate with maximum skin dose (MSD). However, although MSD showed fairly good correlation with KAP and CK, several limitations were identified challenging the set-up of non-centre-specific European alert thresholds. This paper presents preliminary results of this wide European measurement campaign and focuses on the main challenges in the definition of European alert thresholds.

Weighting of secondary radiations in organ dose calculations.

The current system of dose quantities in radiological protection is based, in addition to the absorbed dose, on the concepts of equivalent dose and effective dose. This system has been developed mainly with uniform whole-body exposures in mind. Conceptual and practical problems arise when the system is applied to more general exposure situations where the radiation quality is altered within the human body. In this article these problems are discussed, using proton beam radiotherapy as a specific example, and a proposition is made that dose equivalent quantities should be used instead of equivalent doses when organ doses are of interest. The calculations of out-of-field organ doses in proton therapy show that the International Commission on Radiological Protection-prescribed use of the proton weighting factor generally leads to an underestimation of the stochastic risks, while the use of neutron weighting factors in the way as practised in the literature leads to a significant overestimation of these risks.

Occupational radiation doses in interventional radiology: simulations.

In interventional radiology, occupational radiation doses can be high. Therefore, many authors have established conversion coefficients from the dose-area product data or from the personal dosemeter reading to the effective dose of the radiologist. These conversion coefficients are studied also in this work, with an emphasis on sensitivity of the results to changes in exposure conditions. Comparison to earlier works indicates that, for the exposure conditions examined in this work, all previous models discussed in this work overestimate the effective dose of the radiologist when a lead apron and a thyroid shield are used. Without the thyroid shield, underestimation may occur with some models.

Monte Carlo simulations of occupational radiation doses in interventional radiology.

Occupational radiation doses in interventional radiology can potentially be high. Therefore, reliable methods to assess the effective dose are needed. In the present work, the relationship between the personal dose equivalent, H(p)(10), the reading of a personal dosimeter and the effective dose of the radiologist were studied using Monte Carlo simulations. In particular, the protection provided by a lead apron was investigated. Emphasis was placed on sensitivity of the results to changes in irradiation conditions. In our simulations a 0.35 mm thick lead apron and thyroid shield reduced the effective dose, on average, by a factor of 27 (the range of these data was 15-41). Without the thyroid shield the average reduction factor was 15 (range 6-22). The reduction sensitively depended on the projection and the X-ray tube voltage. The dosimeter reading, when the dosimeter was worn above the apron and a thyroid shield was used, overestimated the effective dose on average by a factor of 130 (range 44-258) when the dosimeter was located on the breast closest to the primary X-ray beam. Without the thyroid shield the average overestimation was 69 (range 32-127). If the dosimeter was worn under the apron its reading generally underestimated the effective dose (on average by 20% with the thyroid shield). Our study indicates that, even though large variations are present, the often used conversion coefficient from the dosimeter reading above the apron to the effective dose, around 1/30, generally overestimates the effective dose by a factor of two or more.